Electronic device for timing toll calls and for signaling both subscriber and operator



'Dec. 12, 1950 H. J. MCCREARY 2,533,677

ELECTRONIC DEVICE FOR TIMING TOLL CALLS AND FOR SIGNALING BOTH SUBSCRIBER AND OPERATOR Filed Sept. 15, 1945 2 Sheets-Sheet 1 INVENTOR. HAROLD J. MC CREARY ATTORN EY Dec. 12, 1950 Y H.VJ. MOCREARY, 2,533,677

' ELECTRONIC DEVICE FOR TIMING TOLL CALLS AND 7 FOR SIGNALING BOTH SUBSCRIBER AND OPERATOR Filed Sept. 15, 1945 2 Sheets-Sheet? FIG. 2

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INVENTOR.

HAROLD J. MG CREARY ATTORN EY Patented Dec. 12, 1950 ELECTRONIC DEVICE FOR TIMING TOLL CALLS AND. FOR SIGNALING BOTH SUB- SCRIBER AND OPERATOR Harold J. McCreary, Lombard, 111., assignor to Automatic Electric. Laboratories, Inc., Chicago, 111., a corporation of Delaware Application September 15, 1945, Serial No. 616,615

4 Claims. 1 The present invention relates in general totelephone systems and, in particular, to improved circuit arrangements for timing toll calls there- In dial switching telephone systems it is the customary practice to permit subscribers to complete connections within a local calling area while calls to other areas requiring a toll char e are completed by an intervening operator. Ordinarily a naught is dialled by the calling party to secure the assistance of an A operator when making a toll call. In response to the extension of a connection to a trunk terminating at the "A switchboard, an operator at that switchboard answers the call by plugging one of hercord circuits into the trunk jack. ihe operator then makes out a toll ticket and proceeds to establish the desired connection by inserting the calling end of the cord circuit intoa jackterminating an outgoing trunk to the desired distant office, and either passing the desired number to an incoming operator thereat or dialling the digits of the desired number. When the called subscriber answers, assuming that the desired connection is successfully completed, the operator notes the time that the conversation starts on the toll ticket. Upon receiving a disconnect signal at the termination of the conversation, the operator again notes the time on the toll ticket.

Usually a charge is made for the initial period of the conversation, which may vary from three to five minutes, and an overtime charge is made for each subsequent period, which subsequent periods are usually shorter than the initial period. oftentimes an operator is requested by a subscriber to interrupt the conversation when the total charge has reached a predetermined. amount. Such special service reduces the efficiency of the operator considerably.

It is accordingly an object of the present. in-. vention toprovide improved timing means for in.- forming both the calling party and the operator of the expiration of the initial time period and each subsequent period of a toll call so that the calling party may terminate the conversation when a predetermined total charge has been reached, and so that the, operators time may be more gainfully employed by reducing the amount; of time spent in supervising each call.

A further object of the. inventionis to provide an improved timing apparatus for:- conversation timing oftoll calls. which is readil adjusted to. different desired durations of, theinitial and: ov er.-. time periods and which requires. little. or no; maintenance.

For a, complete understanding of the invention, reference may be had to the following; description taken in conjunction with the accompanying drawings, in which:

Fig. 1 illustrates, in the form of a schematic diagram, a trunk circuit terminating a trunk to a toll switchboard, which trunk circuit incorporates a novel conversation timing apparatus;

Fig. 2 shows a modification of the timing ape paratus included in Fig. 1; and

Fig. 3 is a trunking diagram illustrating the; use of thetrunk circuit in a, complete switching system.

Briefly described, the invention comprises. an electronic timer which is associated, with an in coming trunk terminating inv an A switchboard. The operation of the timer is initiated by the momentary operation of a key by the operator when a. connection has been completed over the associated trunk and the calledv party has responded.v Inone. form of the timer. three gaseous discharge tubes are. employed. Each; of these tubes has. an aperiodic circuit, comprising a condenser and resistor in. multiple, associated therewith. A source of anode potential, which may be the. usual exchange. battery, is, provided; but is normally disconnected from the tubes. In response. to. the momentary operation, of the key' by the operator, the anode circuit of a. first one of the tubes is. completed simultaneously with the. opening of a charging circuit. for the condenser associated therewith, which. condenser is connected between the control electrode andcathode of the. first tube. The charge on this.

A condenser is such. as to prevent firing. of the first.

tube until the condenser has discharged toa pre. determined potential. The. time required for the discharge of the condenser is determined. by the. value of the. resistor connected in. multiple with the. condenser, by: the capacity thereof, and by thev initial charge impressed thereon. Thus after a predetermined time interval, which isv somewhat. less than the desired initial time period, the first tube. fires and. operates a relay connected in its anode circuit to connectv the source of anode potential to the second and third gas tubes. Each of the second and third tubes has: a similar aperiodic circuit. connected thereto, either one of which may be connected in. a. charging circuit by a relay connectedin the anode circuit of the third tube. The aperiodic circuit associated: with the. second tube is normally connected in. the charging circuit, while that associated with the third tube. is normally disconnected from. the charging; circuit. Thus ste m 3 the third tube fires immediately in response to the operation of the relay connected in the anode circuit of the first tube. The relay in the anode circuit of the third tube operates to transfer the charging circuit from the aperiodic circuit associated with the second tube to that associated with the third tube. In response to the operation of this relay a momentary tone is applied to the trunk to inform the subscribers connected thereto that the initial time period is about to expire. After a predetermined time interval, equal to the difference between the desired initial time period and that which elapsed prior to the application of the warning tone to the trunk, the second tube fires. The anode circuits of the second and third tubes are coupled so as to cause either tube to be extinguished in response to the firing of the other tube. The third tube therefor is deionized and the relay connected thereto released, which causes a supervisory lamp in the operators cord circuit to fiash indicating the expiration of the initial time period. This lamp continues to flash until extinguished by a further momentary operation of the key used to initiate the operation of the timer. The timing apparatus continues to operate in the above manner to periodically transmit a warning tone over the trunk prior to the expiration of each overtime period, and to fiash the cord supervisory lamp upon the expiration of each overtime period. The timer may be released by momentarily removing the answer plug of the cord from its jack. In the modified form of the timing apparatus the second tube is eliminated by switching arrangements which permit the first tube to perform dual functions.

'The operation will now be described in greater detail with reference to the drawings. Fig. 3 illustrates a typical switch train over which toll calls may be completed. In response to the initiation of a call by a subscriber in a branch office, a line finder associates a first selector with the subscribers line in the well known manner. The subscriber then dials an causing the first selector to extend the subscribers line to an outgoing trunk circuit which seizes an incoming trunk circuit in the main ofiice over an interoffice trunk. The incoming trunk circuit, shown in detail in Fig. 1, is seized by the extension of battery and ground thereto over conductors I and 2 through relays in the outgoing trunk circuit located in the branch office. Polarized relay IE9 is energized over conductors I and-2 in series with the left windings of repeating coil 3 and resistor i causing relay I69 to operate and close a circuit to relay I38 at contacts IBI. Relay I39 operates and at contacts I 3I removes ground from the sleeve of jack 5 and closes a circuit to the trunk answer lamp 6. The operator, upon observing the lighted answer lamp, will insert the answer plug of an idle cord circuit into jack 5 thereby causing contacts 1 to close a circuit to relay I59. Relay I53 operates, connects resistor 3 in multiple with relay I69 at contacts I5I, short-circuits resistor at contacts I52, prepares a circuit to relay III; at contacts I54, and closes a circuit to relay I 58 at contacts I55. The decrease in resistance in the circuit bridging conductors I and 2 brings about the operation of a marginal relay in the outgoing trunk circuit at the other end of the inter-ofiice trunk which causes a momentary splash of tone to be transmitted over the trunk to the operator in case the calling party has restricted service.

The operator proceeds to make out a toll ticket 4 and to extend the connection, after having learned the number of the party with whom the calling subscriber wishes to be connected, over a toll trunk and switch train in the desired distant oince. After the connection has been completed and the called party'has answered, the operator momentarily operates key 9 thereby completing a circuit to relay IIB through contacts I54. Relay II9 operates, closes a circuit from ground through the upper contacts of key 9 and through contacts III to the sleeve of jack 5, closes its locking circuit to ground through contacts I53 at contacts II 2, removes negative battery from the upper terminal of condenser ID at contacts I I3, and closes ground, or positive battery, to the anode of tube II through relay I19 at contacts H4. The ground placed on the sleeve of jack 5 7 lights the cord supervisory lamp I2 (Fig. 3) to verify to the operator that the timer has started. The circuit to lamp I2 is opened when key 9 is released.

Condenser I9 is normally charged to a potential equal to the voltage drop across the left portion of potentiometer I3. When negative battery is.

disconnected from the upper terminal of condenser IB it discharges through resistor I4. When condenser I!) has discharged to the striking potential of tube II, it becomes ionized thereby energizing relay I19. Relay I19 operates and at contacts III closes ground through impedances IT and I8 to the anode of tube I5, and through impedance I1 and relay I99 to the anode of tube Iii. The control electrode of tube I5 is normally connected to negative battery at contacts I94 which prevents tube I5 from striking. The condenser I9 connected between the control electrode and cathode of tube I6 is normally discharged, therefore tube It strikes immediately and energizes relay I93. Relay I90 operates, connects a source of tone, not shown, through condenser 29, and contacts I92 and I82 to conductor 2, closes a circuit to slow acting relay I at contacts I93, and transfers negative battery from condenser 2I to condenser I9 at contacts I94. Tube I 6 remains ionized, however, since the control electrode loses control of the tube once it has become ionized. Relay I89 operates after a brief delay and disconnects the tone source from conductor 2 at contacts I82. The momen tary splash of tone placedon the trunk serves to warn the calling and called parties that the initial charge period is about to expire.

Condenser 2| is normally charged to a potential equal to the voltage drop across the left portion of potentiometer 22. When negative battery is removed from the upper terminal of this condenser by the operation of relay I99, condenser 2I commences to discharge through resistor 23. After a predetermined time interval condenser 2I is discharged to the striking potential of tube I 5. When tube I5 fires it causes tube I6 to be' deionized by momentarily lowering the anode voltage thereof. This momentary reduction in the anode potential of one tube in response to the firing of the alternate tube is accomplished by the capacitive coupling'between the two anodes through condenser 24. Relay I90 restores when tube I6 is deionized, closes a circuit from negative battery through resistor 25, contacts I9I and I8I, relay I09, and high resistance 26 to ground, opens the circuit to relay I80 at contacts I93, and transfers negative battery from condenser I9 back to condenser 2| at contacts I94. Relay I00 operates and locks to battery through the cord supervisory lamp I2 and the-sleeve con! 5 ducto-r of the cord at contacts IOI. Relay I80 restores after a brief delay and opens the op, erating circuit to relay I at contacts I8I. Re.- lay I00 holds in series with lamp I2 and high resistance 26, but the current flowing in this circuit is insufficient to light lamp I2. The high resistance 26 is periodically short-circuited by an interrupter 2'! thereby causing lamp I2 to flash on and oil. The flashing of lamp I2 notifies the operator of the termination of the initial charge period. A flashing lamp signal is used to differentiate from a disconnect signal, which is given by a steady lighting of the same lamp when the calling party disconnects. Upon ob! serving the flashing of lamp I2, the operator again momentarily operates key 9. The upper contacts of key 9 short-circuit relay I00 through contacts III and IN. Relay I00 consequently restores. When key 9 is released ground is removed from the sleeve of jack 5 and lamp I2 is extinguished.

During the time that relay I90 was operated it connected negative battery to the upper terminal of condenser I9 causing this condenser to become charged to a potential equal to the voltage drop across the left portion of potentiometer 22. When relay I90 restored at the expiration of the initial charge period it removed negative battery from the upper terminal of condenser I9 which then discharges through resistor 28. After a predetermined time interval, which is somewhat less than the desired overtime period, condenser I9 is discharged to the striking potential of tube I6. Tube I6 fires, deionizes tube I5 by momentarily lowering its plate potential, and operates relay I90. Relays I90 and I80 operate as previously described to impress a splash of tone on the trunk and to initiate the timing of a further brief time interval by condenser 2! and resistor 23. At the end of this further brief time interval tube I5 is fired to deionize tube I6 and thus release relays I80 and I 90. Relay I00 is again operated to flash the cord supervisory lamp, upon the release of relay I90, to indicate the expiration of the first overtime charge period. This same cycle of events will be repeated indefinitely until the timer is released by the operator.

For a given initial charge, the sum of the time constants of the aperiodic circuits associated with tubes I5 and I6 determines the duration of the overtime period and the ratio between the time constants of these circuits determines the amount by which the warning tone precedes the expiration of the time period. If desired, resistors 23 and 23 may be made adjustable to permit independent adjustment of the two portions of each overtime period, The adjustment of potentiometer 22 determines the initial charge on condensers I9 and 2| and thus may be used to vary the duration of the overtime period. Similarly, potentiometer I3 determines the initial charge on condenser I0 and may be varied to change the duration of the initial charge period. The time constants of these aperiodic circuits, and the adjustment of potentiometers I3 and 22, may, for example, be such that tube II fires 1% minutes after relay IIO operates, tube I5 fires 15 seconds after relay I90 operates, and tube I6 fires 45 sec.-. onds after relay I90 restores. The initial charge eriod will then be three minutes and subsequent overtime periods will be one minute. The warning tone will then be given 15 seconds before the expiration of the initial charge period and each subsequent overtime p r Assumin for example, that the time constants T =RQ log. where T i;m in s onds R=resistance in megohms capaci y in roiarads Log.=natural logarithm to base 6 E1=initia1 charge-voltage of C E2=grid to cathode voltage when tube fires Tubes II, I5, and I6 may be of the 2050 type thyratron tubes that fire when their grid to cathode voltage drops to 1 volt. The resistor condenser values of these tube circuits are determined as follows:

Tube 11 Assume that th ba ery vol age is 4 volts. potentiometer l3 may be 500 ohms and tapped at 10 volts from the negative end, relay I10 may hav a 1000 hm. l, the non-d i nat d rid resist r y be ,0 0 ms and he time delay desired is two and three-fourths minutes or 165 ond .From the bovev n f rmu a, the values of resistor I 4 and condenser I0 are determined as follows:

165=RC log.

Condenser I0 can be 10 microfarads and resistor I4 will then be 7.18 megohms.

Tube 15 Assume that the battery voltage is 48 volts, potentiometer 22 may be 500 ohms and tapped at 10 volts from the negative end, impedances I1 and I8 each may have 200 ohm coils, relay I may have a 200 ohm coil, the non-designated condenser on potentiometer 22 may have a value of 10 microfarads, condenser 24 may have a value of .75 microfarad, the nonedesignated grid resistor may be 10,000 ohms and the time delay de, sired is 15 seconds. From the above-given for mula, the values of resistor 23 and condenser 2I are determined as follows:

T 15=RC log. :=.2.3

Condenser 2I can be 1 micro farad and resistor 23 will then be 6.52 megohms.

Tube 16 Assume that the same values are used for tube I6 as were used for tube I5 with the exception 7 that the time delay desired is 45 seconds. From the above-given formula, the values of .resistance 28 and condenser I9 are determined as follows:

Condenser I9 can be 2 microfarads and resistor 28 will then be 9.8 megohms.

The same formula may be applied to determine the values of the resistors and condensers in the tube circuits of tubes II and I6 of Figure 2.

If at any time the operator wishes to release the timer, she may do so simply by momentarily removing the answer plug from jack 1 to thereby release relay I50 which opens the locking circuit to relay I I at contacts I53. When the answer plug is reinserted in jack relay I50 reoperates but relay III) will remain normal. The restoration of relay I I0 opens the circuit to relay I which restores and opens the circuit to relay I90.

7 When the calling party disconnects, the direction of current flow over conductors I and 2 of l the inter-ofiice trunk is reversed. Polarized relay I60 consequently restores and opens the circuit to relay I at contacts I6I. Relay I30 restores and grounds the sleeve of jack 5 at contacts I 3i through contacts IOI to light the cord supervisory lamp I2 continuously. If at this time the operator wishes to recall the calling party, she may operate a ringing key in the cord circuit to energize relay I20 in series with the right windings of repeating coil 3 over the tip and ring conductors of the cord. When relay I20 operates it grounds conductors I and 2 at contacts I2I and I22 to operate a differential relay in the outgoing trunk circuit, which latter relay transmits ringing current over the calling partys line. When the operator removes the answer plug from jack 5 to terminate the connection, the circuit to relay I is opened at contacts 1. Relay I50 restores, opens the circuit to relay I40 at contacts I55, and opens the locking circuit to relay IIO at contacts I53. Relay I40 restores. Relay IIO restores and removes ground from the anode of tube II thus releasing relay I10 which in turn removes ground from the anodes of tubes I5 and I6. Relays I90 and I80 restore in turn, if operated. 4

The modification of the timer shown in Fig. 2 may be substituted for that shown within the dotted lines in Fig. 1. Corresponding reference characters are used in Fig. 2 with primes affixed. In this modification tube I5 of Fig. 1 has been eliminated by employing additional contacts on relay I10, which contacts rearrange the connections of tube II so as to enable it to perform the function of tube I5 in addition to its original function. Thus with relay I10 at normal, tube I I is connected identically to tube II of Fig. 1 through contacts I13, I14 and I15. When tube II fires it energizes relay I10 which operates, closes a locking circuit to its-elf through resistance 29 at its preliminary make contacts I12, transfers the anode of tube II from relay I10 to impedance I8 at contacts I13, transfers thecont o electrode. of tube .1 I. ,from condenser I0 to condenser 2| at contacts I14, and transfers the cathode of tube II from potentiometer I3 to potentiometer 22' at contacts I15. During the movement of the armatures of contacts I13 and I15 from their break to their make contacts the anode circuit of tube II is opened, which causes it to become deionized. Tube II is now connected identically to tube I5 in Fig. 1 and functions in like manner.

' While a particular embodiment of the invention has been illustrated, it should be understood that numerous modifications may be made therein without departing from the true spirit and scope of the invention as defined in the subjoined claims.

What is claimed is:

1. A timing arrangement for measuring elapsed time of telephone conversations over a trunk circuit, a hot-cathode gaseous filled electron dis-. charge device, a biasing circuit for controlling said discharge device, an aperiodic circuit included in said biasing circuit and. comprising a condenser and a resistor connected in multiple, a source of current and a circuit for charging said condenser to a given potential for biasing said discharge device, means for initiating the flow of an aperiodic current in said aperiodic circuit when it is desired to start the timing of an established connection over said trunk circuit by opening said charging circuit to slowly discharge said condenser through said resistor at a given rate to reduce the potential in said biasing circuit, a warning tone circuit, said discharge device operative in response to said reduced potential in said biasing circuit reaching a certain predetermined value, and means controlled responsive to the operation of said discharge device for completing said warning tone circuit to warn subscribers in said connection of the impending expiration of an initial charge period.

2. A timing arrangement for measuring elasped time of telephone conversations over a trunk circuit, a pair of hot-cathode gaseous filled electron discharge devices, a pair of biasing circuits for controlling each of said discharge devices, an aperiodic circuit included in each of said biasing circuits and each comprising a condenser and a resistor connected in multiple, a source of current and an individual circuit for charging each of said condensers to a given potential for biasing each respective discharge device, means for initiating the flow of an aperiodic current in one of said aperiodic circuits when it is desired to start the timing of an established connection over said trunk circuit by opening said charging circuit individual to said one aperiodic circuit to slowly discharge the corresponding condenser through its said resistor at a given rate to reduce the potential in the corresponding biasing circuit, a warning tone circuit, said one discharge device operative in response to said reduced potential in its individual biasing circuit reaching a certain predetermined value, means controlled responsive to the operation of said one discharge device for completing said warning tone circuit to warn subscribers in said connection of the impending expiration of an initial charge period and for initiating the fiow of an aperiodic current in the other of said aperiodic circuits by opening said charging circuit individual to said other aperiodic circuit to slowly discharge the corresponding condenser through its said resistor at a given rate to reduce the potential in the corresponding biasing circuit, a signalling circuit, said other discharge device operative in response to said reduced potential in its individual ibiasing circuit reaching a certain predetermined value, and means controlled responsive to the operation of said other discharge device for completing said signalling circuit to indicate the expiration of the initial charge period.

3. A timing arrangement for measuring elapsed time of telephone conversations over a trunk circuit; a first, a second and a third hotcathode gaseous filled electron discharge device; a first, a second and a third biasing circuit for respectively controlling each of said discharge devices; an aperiodic circuit included in each of said biasing circuits and each comprising a condenser and a resistor connected in multiple, a source of current and an individual circuit for charging each of said condensers to a given potential for biasing each respective discharge device, means for initiating the flow of a first aperiodic current in the aperiodic circuit corresponding to said first biasing circuit when it is desired to start the timing'of an established connection over said trunk circuit by opening said charging circuit individual to said aperiodic circuit to slowly discharge the corresponding condenser through its said resistor at a given rate to reduce the potential in said first biasing circuit, said first discharge device operative in responseto said reduced potential in said first biasing circuit reaching a certain predetermined value, means controlled responsive to the operation of said first discharge device for initiating the flow of a second aperiodic current in the aperiodic circuit corresponding to said second biasin circuit by opening said charging circuit individual to said second aperiodic circuit to v erated responsive to said operation of said second discharge device for completing said warning tone circuit to Warn subscribers in said connection of the impending expiration of an initial charge period and for initiatin the flow Of a third aperiodic current in the aperiodic circuit corresponding to said third biasing circuit by opening said charging circuit individual to said aperiodic circuit to slowly discharge the corre sponding condenser through its said resistor at a given rate to reduce the potential in said third biasing circuit, said third discharge device operative in response to said reduced potential in said third biasing circuit reaching a certain predetermined value, means controlled responsive to the operation of said third discharge device to cause the release of said relay, and a signalling circuit completed in response to the release of said relay to indicate the expiration of the initial charge period.

4. A timing arrangement such as claimed in claim 3, including contacts on said relay controlled responsive to said release of said relay for again initiating the flow of said second aperiodic current.

HAROLD J. McCREARY.

REFERENCES CITED The following references are of record in the file of this patent:

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